1. Field of the Invention
The present invention relates to a semiconductor device, and is applied to, for example, a high-breakdown-voltage transistor which is disposed in a peripheral circuit of a NAND flash memory.
2. Description of the Related Art
Conventionally, a high-breakdown-voltage transistor is disposed between a sense amplifier of a NAND flash memory and a bit line. For example, when the potential of a bit line is raised to an erase voltage Vera that is a high voltage (e.g. about 20V) at a time of a data erase operation of a memory cell, the high-breakdown-voltage transistor is used to cut off a path between the sense amplifier and the bit line (see, e.g. Jpn. Pat. Appln. KOKAI Publication No. 2002-76354, corresponding to no USP).
In the prior art, however, two high-breakdown-voltage transistors having sources commonly connected to two bit lines (e.g. odd/even bit lines) are composed as a single unit. As a result, the area of occupation of the high-breakdown-voltage transistors increases, and this is disadvantageous for microfabrication.
Further, at the time of a write operation of a memory cell, it is necessary to control two gate potentials of the high-breakdown-voltage transistors, and to transfer odd/even bit line potentials to the sense amplifier. However, since there is the need to apply the above-mentioned high voltage, the area of occupation of the high-breakdown-voltage transistors has to be increased, compared to a memory cell, etc., from the standpoint of gate insulation breakdown. If the degree of microfabrication of memory cells increases, the number of bit lines, which need to be gathered, also increases, and the area of occupation of the high-breakdown-voltage transistors, relative to the area of occupation of memory cells, increases. Consequently, the reduction in size of the semiconductor chip is hindered. As described above, the increase in area of occupation of the high-breakdown-voltage transistor has a great influence on the microfabrication of the entire semiconductor device.